*{
    margin: 0;
    padding: 0;
    list-style: none;
}
.main{
    position: relative;
    width: 500px;
    height: 300px;
    background: #ccc;
    margin: 100px auto;
}
.list{
    width: 500px;
    height: 300px;
    position: relative; 
}
.list li{
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    display: none;  
}
.list li:first-child{
    display: block;
}
.list img{ 
    width: 100%;
    height: 100%;
}
.left{
    position: absolute;
    width: 50px;
    height: 50px;
    left: 10px;
    top: 50%;
    transform: translateY(-50%);
    z-index: 10;
    cursor: pointer;
    background-color: #ccc;
    line-height: 50px;
    text-align: center;
    opacity: 0.5;
    display: none;
}
.right{
    position: absolute;
    width: 50px;
    height: 50px;
    background-color: #ccc;
    line-height: 50px;
    text-align: center;
    right: 10px;
    top: 50%;
    transform: translateY(-50%);
    z-index: 10;
    cursor: pointer;
    opacity: 0.5;
    display: none;
}
.round{
    width: 200px;
    height: 30px;

    position: absolute;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;    
    line-height: 30px;
}
.round li{
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: #ccc;
    text-align: center;
    margin: 5px 10px;
    cursor: pointer;
}
.round li.choose{
    background-color: blue;
}